MASTER'S THESIS IN SEDREGROUP

 3D Geomodeling of reservoir outcrop analogs

Luis Miguel Yeste

Abstract:

From geometric, sedimentological and petrological characteristics derived in outcrop and cores and well logging data of boreholes in combination with GPR lines, two 3D models of two examples belonging to the red beds of TIBEM (Triassic of the Iberian Meseta, Spain) is constructed. One of the selected examples corresponds to a meander belt in which the main highly sinuous channel, the point bars associated with the main channel, multiple scroll bars attached to one of the point bars and two chute channels are distinguished for modeling. The other example selected corresponds to a braided system in which two channels and two compound bars are distinguished for modeling. The models have been obtained by applying the Petrel software. Modeling has been carried out by both stochastic and deterministic methods, being the last one which shows quite realistically heterogeneities within the reservoir facies. On the other hand the stochastic methods have differentiate fairly well zones of greater and lesser value porosity and permeability, controlled by the distribution of lithofacies between different sub-environments. These examples are revealed as some interesting similar outcrops analogs to many fluvial reservoirs, demonstrating the usefulness of this research in order to exploit hydrocarbon reservoirs.

3D modeling of multi-scale facies in reservoir analogues. Example in a Triassic meanderbelt system

Luis Miguel Yeste

Abstract: 

From geometric, sedimentological and petrological characteristics derived in outcrop and core and well logging data of 4 boreholes in combination with 5 GPR lines, a 3D model of a layer of sandstone in TIBEM (Triassic of the Iberian Meseta,Spain) is constructed. The selected example corresponds to a meander belt. In it we have distinguished for modeling the main highly sinuous channel, two successive point bars, multiple scroll bars and two chute channels, as well as a clay plug marking the phase of channel inactivity. The model obtained by applying the Petrel software shows fairly realistic heterogeneities within the reservoir, coming to be recognized areas of quite different value of porosity and permeability, controlled by the distribution of lithofacies among different sub-environments. The example is seen as an outstanding outcrop analog to many fluvial reservoirs, showing the interest of this research for the production in both oil reservoirs and clastic aquifers.

Facies analysis of subsurface sandstones from TIBEM

Nelson Gregorio Lizarazo

Abstract:

This behind-outcrop study investigates Triassic fluvial sandstones in the Tabular Cover of the Iberian Meseta, SE Spain (TIBEM) which were deposited in different environmental contexts: meander belts, braidplain and crevasse splay lobes. Outcrop studies combined with coring and logging are widely used to characterize complex stratigraphic variability, this minimizes cost compared to obtaining such information from exploratory wells. Ideally, outcrop information should be presented in familiar formats used for exploration and development, that is, well logs, seismic, cross section and 3D models to bridge the conceptual gap between what is observed in outcrop and what occurs in the subsurface. The TIBEM sandstones may serve as an analogue for reservoir units in other, comparable, continental basins. The present study considers: 1) Drill cores from ten boreholes, four boreholes drilled in a meander belt and six in a braidplain, 2) Acoustic and Optical borehole televiewer data which provide Acoustic Borehole Images (ABI) and Optical Borehole Images (OBI), and 3) Gamma ray and spectral gamma ray logs.

Drill cores description permitted identification of nine lithofacies for meander belt: fine to medium-grained sandstone with clasts on an erosional surface (Ss), very fine to fine-grained horizontal laminated sandstone (Sh), very fine-grained sandstone with ripple cross lamination (Sr), very fine to fine-grained sandstone with epsilon cross bedding and ripple cross lamination (Sla), very fine-grained low-angle cross-bedded sandstone (Sl), medium to coarse-grained trough cross-bedded sandstone (St), horizontal laminated siltstone and claystone (Fl), ripple cross laminated siltstone and claystone (Flr) and massive siltstone and claystone (Fm). Eigth further lithofacies were distinguished for the braidplain: very fine-to fine-grained horizontal laminated sandstone (Sh),very fine to fine planar cross-bedded sandstone (Sp), fine to medium-grained trough cross-bedded sandstone (St), very fine-grained sandstone with ripple cross-lamination and climbing ripples cross-lamination (Sr), horizontal laminated siltstone and claystone (Fl), ripple cross-laminated siltstone and claystone (Flr) and massive siltstone and claystone (Fm).

A set of criteria, based on borehole images, was established to aid in the interpretation of lithofacies. Seven electrofacies were defined from borehole image signatures that represent the most common lithofacies observed in cores from the meander belt by comparing paired, calibrated borehole images and cores. Dip patterns measured in borehole images were used to identify process of lateral and vertical accretions, geometry and paleo-currents of the meander belt and sedimentary structures in both; the meander belt and the braidplain. 

Gamma ray readings were obtained and grouped according to their shape classification to characterize the types of depositional sub-environments in TIBEM. Bell-shaped and egg-shaped gamma ray logs are typical of the channels and crevasse splay lobes of the meander belt (Sequence II) and cylinder-shape gamma ray logs are a distinctive feature of braidplain deposits. Spectral gamma ray logs were useful for establishing the element influencing high gamma ray readings in clean sandstones from the Sequence II.

The reconstruction of the meander belt was undertaken combining interpretation of dip patterns and application of sedimentological concepts. Three dimensional models were constructed considering the thickness variability of the sandstone bodies with ribbon-like geometries, in contrast to the tabular sand bodies of the braidplain deposits.

Petrological and petrophysical study of the Triassic red beds of the Tabular Cover, Iberian Meseta (sector de Alcaraz)

Saturnina Henares

Abstract:

Triassic red beds of the Tabular Cover of the Iberian Meseta (TIBEM) constitute an outcrop analogue of hydrocarbon reservoirs, currently in operation, such as the TAGI in Argelia. Studied outcrop, located in Alcaraz, (Albacete), provides an outstanding example of sandstones embedded in fines deposited in different fluvial sedimentary environments which directly influences their properties as reservoir rocks for fluids (water, oil and gas). Thus, a petrological and petrophysical characterization has been carried out on the most representative sandstone bodies in this area, in order to determine the controlling factors on properties variability. On the basis of the depositional environment and the sedimentary sequence, these deposits are subdivided as follows: overbank deposits (crevasse splay lobes, sheetflood-like deposits and undifferentiated overbanks) and channelized (meandering and straight channels) deposits from sequence II; and braidplain from sequence IV.

In a well-constrained sedimentological framework, petrological study allowed to characterize differences in modal composition and detrital fabric between deposits from different sequences and, within them, between different depositional environments. Accordingly, petrophysical properties such as porosity and permeability also vary, increasing anisotropy and heterogeneity, which can result in the creation of barriers for fluid migration within the sedimentary body. Likewise, performance of several tests using fluids of different viscosity and density has highlighted the influence of fluid physical properties on potential reservoir quality of the rocks with which they are interacting. All this together allowed to classify the studied depositional environments according to their increasing potential as reservoir rock as follows: overbank deposits (crevasse splay lobes, undifferentiated overbanks and sheetflood-like deposits) from sequence II; channelized deposits (meandering and straight channels) from sequence II; and braidplain (sand flat area, channel area and sand flat tail) from sequence IV.